An automatic Physical Cell Identifier (PCID) allocation scheme for configuring a Self-Organization Network (SON) in a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system is under development. In the automatic PCID allocation scheme, a new Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Node-B (eNB, also referred to as a base station (BS)) collects neighbor cell information to select a PCID to be allocated to its own cell. In the LTE system, various cells may be freely established/removed by users. Also, the cell establishment requires a complicated cell driving process using many initial configuration parameters. A scheme is needed in which the eNB automatically determines the initial configuration parameters in such SON environments without the help of an operator. In particular, a scheme is needed that allocates a PCID used by a physical layer for cell identification, among the initial configuration parameters of a new cell. In the LTE system, a plurality of cells reuse five hundred four (‘504’) PCIDs.
Meanwhile, the eNB should consider collision-free conditions and confusion-free conditions for PCID allocation.
FIGS. 1A and 1B illustrate collision-free conditions and confusion-free conditions for Physical Cell Identifier (PCID) allocation.
Referring to FIG. 1A, a collision may occur when cells 100 and 102 neighboring each other (hereinafter also referred to as neighbor cells) use the same PCID to interfere with each other. When the collision occurs, a user terminal 104 cannot discriminate between the cells 100 and 102 and thus experiences difficulty in communicating with the cells 100 and 102. Thus, the collision-free conditions are to restrict the use of the same PCID by the neighbor cells.
Referring to FIG. 1B, cells 110 and 112 use different PCIDs A and B and do not interfere with each other. However, when a cell 114 neighboring the cell 112 uses the same PCID A as the cell 110, a user terminal in the cell 112 may have encounter confusion as to which of the cells 110 and 114 it has to be handed over.
That is, a handover problem may occur when different cells neighboring a common cell use the same PCID. Thus, the confusion-free conditions are to restrict the use of the same PCID by the different cells neighboring the cell.
PCID allocation for an eNB is performed in two stages. First, a candidate PCID list capable of preventing collision/confusion is determined. A new cell may remove a collision/confusion causing PCID from an available PCID list to make the candidate PCID list. Thereafter, the eNB randomly selects a PCID from the candidate PCID list and allocates the selected PCID to the new cell.
Such a random PCID selection method has low complexity. However, the random PCID selection method cannot achieve a system performance gain because PCIDs are randomly allocated to cells.
For example, a WCDMA system allocates a scrambling code. Thus, a scrambling code planning is performed for the efficient use of limited scrambling codes.
In other words, in a CDMA system, because an operator knows coverage information such as antenna patterns and locations of cells to be installed in a cell planning stage, a user may determine a distance between cells capable of using the same scrambling code (i.e., a code reuse distance), in consideration of a cell coverage and a path loss. A code reuse pattern satisfying the determined code reuse distance is predefined in the cell planning stage to allocate a scrambling code to each cell. This method is efficient because a system operation is possible by the available minimum code number when the code reuse distance is determined.
However, a code reuse pattern is difficult to use in the LTE SON environments because cells of various coverages are occasionally established and removed at random locations.
What is therefore needed is a method and apparatus for efficiently allocating a PCID in a wireless communication system by using a code reuse pattern.